出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：The neutral-kaon decay KL is a direct CP-violating process caused by a flavor-changing neutral current, and the branching ratio is predicted to be (2.49±0.39)×10-11 in the Standard Model. The rare decay is one of the processes expected to have a significant impact on new physics searches. The E391a experiment at the KEK 12-GeV proton synchrotron was the first dedicated search for the KL decay. The final results are reported in this contribution. Combining the data sets in February- April 2005 (Run-2) and October-December 2005 (Run-3), the single event sensitivity was 1.1×10-8 and no events were observed in the signal region. The upper limit on the branching ratio was set to be 2.6× 10-8 at the 90% confidence level. The E391a experiment as a whole has improved the limit from the past experiment (FNAL-KTeV) by a factor of 20.
